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I Dark matter and acoustic peaks in the CMB

  1. Jan 9, 2017 #1
    Baryon acoustic oscillations acoustic peaks in cosmic microwave background anisotropies
    provides evidence for cold dark matter

    but is there any sort of prediction as to the specific properties of this dark matter?

    predictions as to the mass of this dark matter, total mass, and mass of the individual particle, i.e 100 gev.

    prediction as to the lifetime? do they have to continue to persist in the universe? could something like neutrons, clusters of neutrons like dineutrons or tetra neutrons, or even neutron stars, create these acoustic peaks, but decay? or neutrinos perhaps forming a condensate that existed in these energies and densities, but then decay shortly

    prediction as to quantity?
    i.e the amount of dark matter required to create CMB accoustic peaks is exactly 5x mass of baryons?

    do the standard candidates cold dark matter WIMPS, Axions, sterile neutrinos all satisfy these constraints?

    is it possible that either known SM particles like neutrons, neutron stars, neutrinos, or even something like strangelets can satisfy this dark matter and create acoustic peaks in CMB, or something like quantum mechanical black holes, primordial black holes, or gravity in theories like MOND or Verlinde, create these oscillations?

    asymptotic safety in gravity scenarios, and Verlinde and MOND, suggest there's only modification of gravity to explain galaxy rotation curves, not dark matter. there's only the SM, or some minimal extension of the SM. the most common objection is acoustic peaks in CMB.

    if a tetraneutron is stable, long enough during CMB oscillations, could tetraneutrons cause acoustic peaks, so that there's no reason to modify SM, then invoke Verlinde/MOND to explain galaxy rotation

    Last edited: Jan 9, 2017
  2. jcsd
  3. Jan 11, 2017 #2


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    The total amount of dark matter is an experimentally parameter in the lambdaCDM standard model of cosmology, rather than a parameter which is predicted. The amount of DM parameter is set (in concert with the setting of several other lamdaCDM parameters) based upon observations such as CMB and BAO observations.

    The observations themselves, of course, are not models and therefore do not make predictions. Only models, such as the lambdaCDM model which is used to explain CMB and BAO observations, can make predictions, and the total amount of dark matter is something that it determines based upon observations, not something that it predicts in advance. It has formulas for converting observations into a total amount of dark matter that would be consistent with those observations, but it says too little about the nature of dark matter to provide any way to independently test the accuracy of that conversion.

    For example, based upon CMB and BAO observations, and upon observations of the rotational dynamics of the Milky Way, we can predict how much dark matter should pass through the Earth in any given period of time at (at least) an order of magnitude level. And, given that knowledge, we can predict how much of a signal a dark matter detector should generate for any given cross-section of interaction with ordinary matter. But, if that cross-section of interaction is zero (which would be perfectly consistent with the lambda CDM model and all other observations of dark matter phenomena), then dark matter detectors shouldn't see anything. All the lambdaCDM model assumes is that the cross-section of interaction of dark matter should be no stronger than that of neutrinos, and indeed, if dark matter exists at all, we know from direct dark matter detectors and collider experiments, that its cross-section of interaction with ordinary matter must be much smaller than a neutrino's weak force coupling.

    The lambdaCDM model assumes that dark matter is at least very nearly stable, almost collisionless, lacks interactions via the strong or EM forces, and is not relativistic in velocity. The model makes no other assumptions about the properties of dark matter.

    Astronomy observations have recently confirmed what the lambdaCDM model only assumes. Any dark matter candidate must have a mean lifetime for each particle, at least, on the order of the lifetime of the universe in most kind of dark matter models.

    People who look at dark matter phenomena at the galaxy level distinguish between "warm dark matter" (which has a bit higher average velocity) and "cold dark matter" (which has a bit lower average velocity). Both both WDM and CDM count as cold dark matter for the purposes of definition of dark matter used in the lambdaCDM standard model of cosmology and are indistinguishable from each other for those purposes.

    In most (but not all) dark matter models, there is a functional relationship between dark matter particle mass and dark matter particle average velocity. In such models, dark matter particles must be much more than 1 eV in mass, but that is pretty much the only mass constraint on dark matter and the mass constraint can be overcome, for example, in all models, such as the axion dark matter model, where the often assumed functional relationship between dark matter particle mass and dark matter particle average velocity does not hold.

    No. The lamda CDM model considers baryonic matter and neutrinos separately from dark matter and they have different properties in the model. Neutrinos are "hot dark matter" which is inconsistent with observation, because it is mostly relativistic in velocity which would lead the universe to be much less clumpy than it is in reality (also we can directly measure how many neutrinos are flowing through space and the amount doesn't come close to matching the necessary quantity of DM). Baryonic matter is nearly collisionless so it doesn't behave in the manner required.

    Yes. There are many, many dark matter candidates that can satisfy the lambda CDM requirements to produce observed CDM and BAO observations. These candidates fail for other reasons. The main reasons are:

    1. Any particle that interacts via the weak force should have been detectable in direct dark matter detection experiments and colliders, but has not been detected.

    2. Most cold dark matter candidates are "too cold" (i.e. have too low average velocities) to reproduce the galaxy scale structure we see in the universe. For example, dark matter that cold would produce more small satellite galaxies and would have different shaped dark matter halos than what is observed.

    In the most popular dark matter models, there is a functional relationship between dark matter particle mass and average dark matter particle velocity. In those models, dark matter simulations tend to prefer a dark matter particle mass on the order of 1-10 keV.

    Other general problems with dark matter particle models are the excessive of observed clusters colliding with each other at high velocities, http://dispatchesfromturtleisland.blogspot.com/2017/01/the-bullet-cluster-as-support-for.html and the excess number of bulgeless disc galaxies that are observed.

    But, the functional relationship does not apply in all dark matter models and another way which might possibly overcome the problems associated dark matter candidates being "too cold" is that dark matter may have a fifth force interaction with other dark matter via a massive boson with a strength roughly on the order of magnitude of the electromagnetic force (this massive force carrier boson usually in the 100s of MeV mass scale is often called a "dark photon").

    No. These possibilities have been basically ruled out. (There is a tiny bit of parameter space left where primordial black holes can't be completely ruled out if you view the evidence in a very generous way, but this is a very disfavored possibility given current evidence.)

    There are modified gravity theories that can create these oscillations. MOND itself is a toy model that doesn't generalize to relativistic applications, and I don't know if the cosmological implications of its relativistic extension has been worked out in terms of CMB and BAO predictions, and Verlinde's model hasn't been operationalized at all. But, there are modified gravity theories, such as Moffat's MOG theory for which cosmological implications for CMB and BAO have been worked out that do create these oscillations.


    This is not an accurate statement. Many modified gravity theories simply haven't been evaluated one way or the other from a cosmology and CBM perspective. I do not recall seeing a single paper out of hundreds that I have briefly looked at, that has ruled out a modified gravity theory based upon its failure to produce acoustic peaks in CMB, although I can't rule out the possibility that there are some such papers somewhere.

    Usually, objections to modified gravity theories are based on Occam's Razor, on the grounds that they have internal theoretical inconsistencies, or on the grounds that they do not accurately predict dark matter phenomena other than galactic rotation curves.

    For example, while MOND and its relativistic generalizations accurately describe galactic rotation curves, it requires additional dark matter or non-luminous ordinary matter of the type you discuss in your initial post, to explain phenomena at the scale of galactic clusters. But, there are other modified gravity theories that do not have this defect.

    No. A gravity modification that would explain galaxy rotation would also dramatically impact CMB and BAO observables. And, a tetraneutron is not a viable possible source of the observed features of CMB and BAO observables. Among other reasons, tetraneutrons aren't a viable possibility because the total baryon budget in the universe is known as there aren't enough baryons in the universe to produce the effects observed.
    Last edited: Jan 11, 2017
  4. Jan 11, 2017 #3
    welcome back ohwilleke ive not seen or heard from you in months. since uve been gone ive had some posts and heard from other posters.

    i'm well aware of the standard cdm type theory. my post is based on some of verlinde's newest paper on entropic. he wants to do away with dark matter and say the effects are better explained in terms of entropic gravity. stacy mcgaugh et al also think modified gravity is a better candidate.

    if we take as a starting point ONLY emergent gravity that gives MOND like effects and the SM, obviously the big bang theory and cdm would be ruled out and a different theory would have to be entertained.

    one objection steve carrol makes to MOND, though he admits he did not read verlinde's paper, is BAO in the CMB.

    how do we know BAO in CMB using an emergent gravity can be the result of specifically quantum mechanical black holes or clumps of neutrons or even stranglets. all of which are all SM type matter.

    verlinde states that finding dark matter would invalidate his theory since the point of his theory of gravity is to make dark matter superfluous.

    don't forget neutrons or tetraneutrons are unstable and will decay into standard baryons.

    the budget of baryons and mass energy of the universe would have to be rethought in an EG scenario.
  5. Jan 11, 2017 #4


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    Thanks for the welcome. I appreciate it. I've been busy on other projects and also took a long vacation. I do have a science blog at http://dispatchesfromturtleisland.blogspot.com/ which you are welcome to comment at if you want to get in touch, or if you just want to see what I'm writing about in the physics area which makes up about half the posts at that blog.

    No. CDM would be ruled out, but all modified gravity theories which are sufficiently fleshed out to have a cosmology aspect have either a big bang theory, or suppose a "bouncing cosmology" in which there was a universe before the big bang that got very, very small and then exploded outward again that differ materially from the big bang theory only in the nature and timing of what happens in the first few minutes of the usual GR big bang theory.

    All modified gravity theories, Verlinde's included, are merely modifications of general relativity that share more of its basic features (as they must, because the basic features of general relativity have been well established experimentally).

    I wouldn't take the objections of someone who hasn't even read the damn paper, to a paper that proposes a modified gravity theory that isn't even expressed in an operational manner, very seriously.

    I assume that you mean, "cannot" and the answer is that there isn't enough of it for it to be produced by baryonic matter, that baryonic matter doesn't behave in the manner that dark matter needs to in order to reproduce observed phenomena, and that a black hole solution has been ruled out observationally. See, ruling out black hole solutions, for example, this paper: https://arxiv.org/abs/1612.00457

    He admits more than he needs to, but yes, that is sort of the whole point of the enterprise.

    Neutrons are standard baryons. And, at any energy scale at which neutrons can be formed at all, we know from collider experiments that baryon number is conserved. Therefore, there is no possible way that we could have enough baryons in the universe to produce the observed phenomena attributed to dark matter which takes five times as much mass as the total baryon budget of the universe.

    The mass energy of the universe would indeed have to be rethought in an EG scenario. But, the baryon budget of the universe would not be materially impacted by an EG scenario because we calculate that using multiple different methodologies, many of which (e.g. figuring out how many luminous stars there are in the universe, converting that to baryons, and adjusting for non-luminous baryonic matter), are insensitive to something like a modified gravity scenario. These predictions are robust because they come out roughly the same when calculated using wildly different methodologies.
  6. Jan 11, 2017 #5
    well welcome back. in the verlinde thread on his lates paper someone posted sean carroll's video here. sean's comments were on MOND generally, of which Verlinde reduces to.

    if we accept some form of EG-MOND type scenario, the entire CDM including its accounting of cold dark matter has to be thrown out. so take galaxy rotation curves, in EG-MOND, there is ZERO dark matter. galaxy rotation curves is explained solely in terms of baryon.

    so the entire standard big bang and its claims of dark matter has to be thrown out.

    the probems with paper you linked

    Searching for Primordial Black Holes in the radio and X-ray sky
    Daniele Gaggero, Gianfranco Bertone, Francesca Calore, Riley M.T. Connors, Mark Lovell, Sera Markoff, Emma Storm
    (Submitted on 1 Dec 2016)

    We model the accretion of gas on to a population of massive primordial black holes in the Milky Way, and compare the predicted radio and X-ray emission with observational data. We show that under conservative assumptions on the accretion process, the possibility that O(10)M⊙ primordial black holes can account for all of the dark matter in the Milky Way is excluded at 4σ by a comparison with the VLA radio catalog at 1.4 GHz, and at more than 5σ by a comparison with the NuSTAR X-ray catalog (10 - 40 keV). We also propose a new strategy to identify such a population of primordial black holes with more sensitive future radio and X-ray surveys.

    is the statement "the possibility that O(10)M⊙ primordial black holes can account for all of the dark matter in the Milky Way"

    since in Verlinde-EG MOND black holes don't have to account for most, if any dark matter in the Milky way or any galaxy.

    what is attributed to dark matter is gravity behaving in new ways.

    One Law To Rule Them All: The Radial Acceleration Relation of Galaxies
    Federico Lelli (1), Stacy S. McGaugh (1), James M. Schombert (2), Marcel S. Pawlowski (1, 3) ((1) Case Western Reserve University, (2) University of Oregon, (3) University of California, Irvine)
    (Submitted on 27 Oct 2016)
    We study the link between baryons and dark matter (DM) in 240 galaxies with spatially resolved kinematic data. Our sample spans 9 dex in stellar mass and includes all morphological types. We consider (i) 153 late-type galaxies (LTGs; spirals and irregulars) with gas rotation curves from the SPARC database; (ii) 25 early-type galaxies (ETGs; ellipticals and lenticulars) with stellar and HI data from ATLAS^3D or X-ray data from Chandra; and (iii) 62 dwarf spheroidals (dSphs) with individual-star spectroscopy. We find that LTGs, ETGs, and "classical" dSphs follow the same radial acceleration relation: the observed acceleration g_obs correlates with that expected from the distribution of baryons over 4 dex. Ultrafaint dSphs extend the relation by a further 2 dex and seem to trace a flattening at g_obs~10^-11 m/s^2. The radial acceleration relation exists for any plausible choice of the stellar mass-to-light ratio. For our fiducial values, the relation coincides with the 1:1 line (no DM) at high accelerations but systematically deviates from unity below a critical scale of ~10^-10 m/s^2. The observed scatter is remarkably small (~0.13 dex) and largely driven by observational uncertainties. The residuals show no correlations with other properties like radius, stellar surface density, or gas fraction. The radial acceleration relation is tantamount to a Natural Law: when the baryonic contribution is measured, the rotation curve follows, and vice versa. This local scaling law subsumes and generalizes several well-known dynamical properties of galaxies, like the Tully-Fisher and Faber-Jackson relations, the "baryon-halo" conspiracies, and Renzo's rule.
    Comments: Submitted to ApJ (20 pages, 11 figures, 4 tables). Figure 10 summarizes the key result. A movie is available at this http URL
    Subjects: Astrophysics of Galaxies (astro-ph.GA)
    Cite as: arXiv:1610.08981 [astro-ph.GA]
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